The present invention relates generally to magnetic resonance imaging (MRI) and in particular to imaging techniques using pulse sequences that enable quantitative magnetic resonance imaging relaxometry, including T1rho and T2, for a tissue (such as liver tissue) with suppression of blood signal.
Liver fibrosis is a key feature in most chronic liver diseases. It can lead to liver cirrhosis, terminal liver failure, and hepatocellular carcinoma. Currently, the preferred technique for diagnosis of liver fibrosis is a biopsy. Biopsies, however, are invasive and carry risks of various complications. Noninvasive alternatives would be desired, but so far, they are not sufficiently robust or reliable.
Magnetic resonance imaging (MRI) provides the promise of a noninvasive diagnostic technique that can allow assessments of the composition and state of various tissues. In an MRI procedure, a patient is placed in a strong longitudinal magnetic field that aligns nuclear spins of atoms in the patient's body, producing a net magnetization vector. Radio frequency (RF) pulses with magnetic field components transverse to the longitudinal field and frequencies tuned to the Larmor frequency of an isotope of interest (often 1H) are applied. These pulses can flip spins into a higher energy state, resulting in a transverse component to the magnetization vector. As these spins return to the ground state, responsive signals from the patient's body can be detected. Based on the response to the RF pulses, characteristics of the magnetization can be measured. Commonly used measurements include the spin-lattice relaxation time (T1), measurement of which is typically based on recovery of the longitudinal component of the magnetization vector, and the spin-spin relaxation time (T2), measurement of which is typically based on decay of the transverse component of the magnetization vector. Since different anatomical structures have different material compositions, quantification of T1 and/or T2 can provide information about the material composition of a structure being imaged, and particular pulse sequences can be optimized to quantify T1 or T2. Mill has been used to achieve high-resolution images of a variety of anatomical structures, including organs such as the liver. However, existing Mill pulse sequences have not proven reliable for detecting liver fibrosis, particularly in early stages.